1. Field of the Invention
This invention relates to a surface inspection method, and an apparatus for the method, for inspecting fine foreign matters and defects on a semiconductor substrate (semiconductor wafer).
2. Description of the Related Art
Defect inspection for inspecting foreign matters adhering to a surface of a semiconductor substrate (semiconductor wafer) and scratches occurring during processing has been carried out in a fabrication line of the semiconductor substrate to monitor a occurrence state of dust in production setup. In a semiconductor substrate before the formation of a circuit pattern, for example, fine foreign matters and defects of below dozens of nm must be detected.
In the inspection of the surface of the semiconductor substrate, crystal defects existing in a shallow region in the proximity of the substrate surface and surface coarseness of the substrate surface are also the inspection objects besides the foreign matters and defects.
A customary technology for detecting foreign defects on the surface of the inspection object such as the semiconductor substrate is described in U.S. Pat. No. 5,798,829, for example. This technology fixedly irradiates a condensed laser luminous flux to the surface of the semiconductor substrate, detects scattered light occurring from foreign matters adhering to the semiconductor substrate and inspects the foreign matters and the defects of the entire surface of the semiconductor substrate through rotation and parallel movement of the semiconductor substrate.
A concave mirror using a rotary elliptic surface as a reflecting surface is used for detecting scattered light. The detection position on the semiconductor substrate is set to the first focal point of the ellipsis and a light reception surface of a light reception device is set to the second focal point so that scattered light occurring from the foreign matter can be condensed at a broad cubic angle and fine foreign matters can be detected, too. In this way, the prior art technology does not azimuth-wise isolate and detect scattered light emitted from the foreign matter and defect in all the azimuth directions but collectively condenses and detects the scattered light.
On the other hand, JP-A-2001-255278 discloses a technology that arranges condenser lenses and optical detectors in directions of a plurality of azimuth angles with respect to the surface of a semiconductor substrate and detects scattered light condensed by the condenser lens by an optical detector in accordance with a scattering azimuth. This technology can carry out detection in an advantageous azimuth direction in match with radial direction distribution characteristic of the scattered light from the fine foreign matter.
The technology described in JP-A-2002-188999 detects scattered light from a surface of a semiconductor substrate from all azimuth directions by using one parabolic surface mirror with respect to the surface of the semiconductor substrate.